Emulsifiers derived from hydroxycarboxylic acids

ABSTRACT

Emulsifiers are made by esterifying one or two of the carboxyl groups of citric acid with a hydroxy-ester formed from a long chain alcohol and an acid of formula:   in which R1 and R2 are each hydrogen or methyl.

United States Patent n 1 David et al.

[4 1 Dec. 30, 1975 EMULSIFIERS DERIVED FROM HYDROXYCARBOXYLIC ACIDS Inventors: Reginald David, Lyon; Jean Estienne, Ternay, both of France Assignee: Rhone-Poulenc, S.A., Paris, France Filed: May 28, 1974 Appl. No.: 473,828

Foreign Application Priority Data May 30, 1973 France 73.19733 US. Cl 260/484 A; 260/484 R; 426/202 lnt. Cl. C07C 69/68 Field of Search 260/484 A References Cited UNITED STATES PATENTS 1 H1957 Mchltretter 260/484 A 3,846,479 11/1974 Zech ..260/484A Primary ExaminerLorraine A. Weinberger Assistant Examiner-Paul J. Killos Attorney, Agent, or FirmSte'ven's, Davis, Miller & Mosher [57] ABSTRACT HO COOH in which R and R are each hydrogen or methyl.

1] Claims, No Drawings EMULSIFIERS DERIVED FROM HYDROXYCARBOXYLIC ACIDS The present invention relates to esters of hydroxycarboxylic acids useful as emulsifiers.

The present invention provides new emulsifiers derived from citric acid, a hydroxycarboxylic acid of formula:

1 HOi-COOH and forms, with alcohols, mono, diand tri-esters. Lactic acid has the formula CH Cl-lOl-l COOl-l, and is capable of forming esters with both acids and alcohols, including an ester with itself, called lactyl lactic acid having the formula:

CH CHOH COO CH(CH COOH.

The citric acid esters of the invention have the formula:

il-fi-COOX HO COOY in which each of X, Y and Z represents:

a. hydrogen, alkali metal, or ammonium; or b. a radical of formula:

in which n is l to 2, R and R which may be identical or different, are each hydrogen or methyl, and R is a saturated or unsaturated aliphatic radical of 12 to 22 carbon atoms, one to two of X, Y and Z conforming to definition (a), and the remainder conforming to definition (b).

These esters possess valuable surface-active properties and can, because of this, be used as emulsifiers or dispersing agents in, for example, the foodstuffs industry, the dairy industry, the confectionery industry, and in cosmetology. They are suitable for preparing stable emulsions of the oil-in-water or water-in-oil types; They can thus be used in the preparation of sauces, mayonnaiscs and other compositions rich in fatty constituents. They are also useful in the preparation of animal feedstuffs, such as, for example, milks into which fatty constituents such as animal fat or some other edible fatty constituent have been reintroduced. They improve the wcttability of various ingredients employed in aqueous media, for example powdered milks, dehydrated vegetables, and powdered eggs.

The esters of formula I are prepared, in accordance with the invention, by esterifying a hydroxy-carboxylic acid of the formula:

in which n, R, R and R are as hereinbefore defined with citric acid in a molar ratio of substantially 1:1 to 2:1.

The hydroxycarboxylic acids used in making the new emulsifiers are acids such as glycollic acid, lactic acid and a-hydroxyisobutyric acid. Lactic acid and lactyllactic acid are very particularly suitable because of their accessibility. With fatty alcohols, they form alkyl lactates and lactyl-lactates which can themselves be esterified by a carboxylic acid. In the present case, when citric acid is reacted with, for example, an alkyl lactate, it is possible to produce essentially only citrate monoesters or only citrate diesters depending on the method used, which is described below. These esters have the respective formulae:

H COOH and/or H COOH and/or HO COOH H COO-CH(CH )COOR (III) In order to produce preferentially the monoesters of the formula II, it is necessary to react citric acid with the alkyl lactate in substantially equimolecular amounts, while in order to produce the diesters of the formula Ill, twice as much alkyl lactate as citric acid, in mols, is used. It is possible to use larger amounts of alkyl lactate, but this is not desirable because a large amount of the triester then forms, which does not possess as good surface-active properties as those of the monoesters or diesters.

The alcohol of formula ROH may be, e.g., dodecyl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol or an other alcohol which originates, for example, from thesaponification of natural fatty materials. The lactates of these alcohols are known, and can be obtained by heating substantially equimolecular amounts of lactic acid with the alcohol, removing the water as it'i: formed. It is also possible to use esters of such alcohol: with lactyl lactic acid, which are also known compounds obtained by reacting lactic acid and the alcoho ROH in a molar ratio of 2 l.

The esters of the formula 11 are prepared by heating citric acid with the alkyl lactate or other esters of formula:.

.n a molar ratio oflactate (or other ester) to acid of 0.8 l to 1.2 1, and preferably 1 1. The reaction is pref- :rably carried out at l170C, and especially at l 40160C, under a reduced pressure of nitrogen or :ome other inert gas. During this heating, the water of :rystallisation of citric acid (in the case .where a comnercial crystalline product is employed) and the water 'esulting from the esterification are removed. The reaci on is usually carried out without a diluent, but an inert liluent' may be used if desired.

The-esters of the formula III are prepared under the ame conditions, but the molar ratio of lactate (or vther ester) to acid is from 1.8 1 to 2.2 1, and preferlbly 2 1. In both cases, it is the molar ratio of the eagents employed which essentially determines vhether monoesters or diesters are formed prepondervntly.

In an alternative method, the citric acid, lactic acid r other hydroxy carboxylic acid, and the alcohol are eacted together simultaneously in a molar ratio suitble for producing the desired ester. The reaction is arried out under the same working conditions as those ldicated above for the reaction of citric acid with the lkyl hydroxy carboxylate. By this one-stage process, roducts with a high citrate monoester or diester con- :nt are obtained.

Whichever preparation method is used, the products btained are odourless waxes which melt at temperarres of the order of to 55C and are soluble in the sual solvents such as ketones, like acetone and methyl thyl ketone, alcohols, e.g. ethanol, benzene, petro- =um ether and ethyl ether. They are miscible with fatty laterials. Because'of the acidity imparted to them by 1e presence of the non-esterified acid groups, they can )rm salts. Thus with alkaline reagents such as sodium ydroxide, potassium hydroxide, ammonia solutions 1d alkali metal carbonates and bicarbonates, they arm salts which are solids which are soluble in water 1d which also possess emulsifying properties. Such lltS are preferably made in a dilute medium 'and under )ld conditions in order to prevent saponification of ie citrate ester. An advantageous process for the prepation of these salts consists of reacting an aqueous ilution of the alkaline reagent with the citric acid ester ssolved in a water-miscible solvent. The salt formed 'ecipitates' and may then be isolated from the aquels-organic phase by any known means.

The following examples illustrate the invention.

EXAMPLE 1 '4 reaction mixture is then allowed to cool to 110C and poured onto a borosilicate glass plate where it cools to ambient temperature. 170.25 g of octadecyl lactate are thus obtained as a creamy-white waxy product, m.p. 3840C (KOFLER). This product has the formula CH CHOH COO c n an acid number of 4.5 and an ester number of 157.5.

b. 102.6 g (0.3 mol) of octadecyl lactate are introduced into an identical apparatus and are heated to 60C over the course of 15 minutes. 63 g (0.3 mol) of citric acid monohydrate crystals are then added and the apparatus is purged with nitrogen. The temperature is raised to 156C over the course of 40 minutes while the apparatus is gradually evacuated to mm Hg. Heating is continued, with vigorous stirring, for 1 hour 40 minutes, to maintain the temperature at l160C, the mixture is then allowed to cool to C, and the vacuum is broken. The homogeneous reaction mixture, of

orange-yellowcolour, is poured onto a borosilicate glass plate and left to stand at ambient temperature. 144.2 g of a yellow waxy product, m.p. 4850C (KO- FLER), are thus obtained. It has an acid number of 204 and an ester number of 218. It consists essentially of the octadecyl lactate citrate.

c. 55 g (0.1 mol) of the citrate ester are introduced into a 600 cm beaker equipped with an anchor stirrer, and are dissolved in 183 cm of acetone by heating at 30C. The solution is then cooled to 20C and, while stirring vigorously, 200 cm of N aqueoussodium hydroxide solution are run in, while the temperature is kept at 2025C by an ice bath. ,A precipitate forms and the mixtureis cooled to, 5C for.3O minutes. The precipitate is filtered off, drained and then dried to constant weight in an oven at 30C, under the vacuum provided by a water pump. 51.7 g of a yellow solid product with an acid number of 21 and an ester number of 179, which is the disodium salt of octadecyl lactate citrate, are thus obtained.

By treating 55 g of the citrate ester obtained in (b) with 100 cm of N aqueous sodium hydroxide solution, in the same way, the corresponding monosodium salt, which has an acid number of 137 and an ester number of 158, is obtained.

EXAMPLE 2 Following the procedure of Example 1, 102.3 g of 88% pure lactic acid (1 mol) are reacted with 242.5 g of hexadecanol (1 mol), and 310.5 g of hcxadecyl lactate with an acid number of 5 and an ester number of 166 are obtained; 1

g (0.35 mol) of hexadecyl lactate are then reacted, under the conditions described in Example 1 (b), with 73.5 g (0.35 mol) of citric acid monohydrate. 153.5- g of an orange-yellow waxy product, m.p. 3840C (KOFLER), with an acid number of 187 and an ester number of 233, are obtained. This product consists essentially of hcxadecyl lactate citrate.

By treating this product with N aqueous sodium hydroxide solution in accordance with the conditions of Example 1 (c), the corresponding monosodium and disodium .salts are prepared, which have respectively acid numbers of 61 and 18 and ester numbers of 224 and 201.

EXAMPLE 3 tate of the formula a CH3 CHOH COO CH(CH COO is zn are obtained. I

124 g of this product (0.3 mol) are then reacted under the conditions of Example 1 (b)with 63 g (0.3 mol) of citric acid monohydrate. A yellow wax which melts at 42-45C, has an acid number of 168 and an ester number of 286, and consists essentially of octadecyl lactyl-lactate citrate, is thus obtained.

Treatment of this wax with an aqueous solution of sodium hydroxide yields the monosodiumand disodium salts, the acid numbers of which are respectively 94 and 51 and the ester numbers of which are respectively 238 and 216.

EXAMPLES 4 to 7 Working under the conditions of the preceding Examples, 0.15 mol of citric acid is reacted with 0.3 mol of each of the lactate esters prepared above, namely: hexadecyl lactate, hexadecyl lactyl-lactate, octadecyl lactate and octadecyl lactyl-lactate. The four products given in the table below are thus obtained. Salification of these products with N aqueous sodium hydroxide solution gives their sodium salts.

EXAMPLES 8 to These Examples illustrate the one-stage preparation of the citrate esters. The preparation is carried out under the conditions of Example 1 (b), by heating directly citric acid, lactic acid and hexadecanol or octadecanol, in molar ratios chosen according to the ester desired. The temperature is kept at 150 l60C for approximately 2 hours minutes. The esters obtained are salified with an aqueous solution of sodium hydroxide under the conditions of Example 1 (c).

The table below gives the various products obtained, their acid and ester numbers, and the molar ratio of the starting materials in the order, citric acid, lactic acid, and hexadecanol or octadecanol.

'-continued Ex Molar i Acid Ester ratio" "s number number 14' um Bis(h'exadecyllactyl- 63 318 lactate)citrate sodium salt 23 271 15 [24:2 Bis(octadecyl lactyl- 71 304 lactate) citrate sodium salt 29 252 EXAMPLE l6 This Example illustrates the emulsifying power of the new compounds by the following test: g of refined suet (or some other fatty material) at 60C are introduced into a 400 cm beaker, 3 g of the product to be tested are dissolved therein, and cm of water at 60C are then added. This mixture is stirred for 30 seconds with a propeller mixer and then transferred immediately to a 250 cm graduated cylinder, kept at 60C. The stability of the emulsion is evaluated by measuring the volume of water which has separated out after various time intervals.

The results obtained are given in the following table, wherein the percentage of water which has separated out, expressed as volume of water which has separated out/volume of water introduced X 100, is shown after 15 minutes, 30 minutes and 1 hour.

The last two lines of the table refer to tests which show that (under the conditions of the test) octadecyl lactate and dioctadecyl citrate do not make it possible to produce stable emulsions of fatty materials in water.

We claim:

1. A citric acid ester of the formula:

H, co0x HO- COOY Pl -C002 in which each of X, Y and Z represents:

a. hydrogen, alkali metal, or ammonium; or b. a radical of formula:

7 in which n is l to 2, R and R which may be identical or different, are each hydrogen or methyl, and R is a saturated or unsaturated aliphatic radical of 12 to 22 carbon atoms, one to two of X, Y and Z conforming to definition (a), and the remainder conforming to definition (b).

2. An ester according to claim 1 in which one of R and R is methyl and the other is hydrogen.

3. An ester according to claim 1 in which R is hexadecyl or octadecyl.

4. An ester according to claim l selected from the class consisting of hexadecyl lactate citrate and its alkali metal and ammonium salts.

5. An ester according to claim 1 selected from the class consisting of bis(hexadecyl lactate) citrate and its alkali metal and ammonium salts.

6. An ester according to claim 1 selected from the class consisting of octadecyl lactate citrate and its alkali metal and ammonium salts.

7. An ester according to claim 1 selected from the class consisting of bis(octadecyl lactate) citrate and its alkali metal and ammonium salts.

8. An ester according to claim 1 selected from the class consisting of hexadecyl lactyl-lactate citrate and its alkali metal and ammonium salts.

9. An ester according to claim 1 selected from the class consisting of bis(hexadecyl lactyl-lactate) citrate and its alkali metal and ammonium salts.

10. An ester according to claim 1 selected from the class consisting of octadecyl lactyl-lactate citrate and its alkali metal and ammonium salts.

11. An ester according to claim 1 selected from the class consisting of bis(octadecyl lactyl-lactate) citrate and its alkali metal and ammonium salts. 

1. A CITRIC ACID ESTER OF THE FORMULA
 2. An ester according to claim 1 in which one of R1 and R2 is methyl and the other is hydrogen.
 3. An ester according to claim 1 in which R is hexadecyl or octadecyl.
 4. An ester according to claim 1 selected from the class consisting of hexadecyl lactate citrate and its alkali metal and ammonium salts.
 5. An ester according to claim 1 selected from the class consisting of bis(hexadecyl lactate) citrate and its alkali metal and ammonium salts.
 6. An ester according to claim 1 selected from the class consisting of octadecyl lactate citrate and its alkali metal and ammonium salts.
 7. An ester according to claim 1 selected from the class consisting of bis(octadecyl lactate) citrate and its alkali metal and ammonium salts.
 8. An ester according to claim 1 selected from the class consisting of hexadecyl lactyl-lactate citrate and its alkali metal and ammonium salts.
 9. An ester according to claim 1 selectEd from the class consisting of bis(hexadecyl lactyl-lactate) citrate and its alkali metal and ammonium salts.
 10. An ester according to claim 1 selected from the class consisting of octadecyl lactyl-lactate citrate and its alkali metal and ammonium salts.
 11. An ester according to claim 1 selected from the class consisting of bis(octadecyl lactyl-lactate) citrate and its alkali metal and ammonium salts. 